Process for producing acrylic synthetic fibers of noncircular cross-section and with improved sparkle

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR PRODUCING ACRYLIC SYNTHETIC FIBERS OF A NONCIRCULAR CROSS-SECTION, IMPROVEED IN SPARKLE, FROM A SPINNING SOLUTION PREPARED BY DISSOLVING AN ACRYLIC POLYMER IN AN INORGANIC SOLVENT MORE PARTICULARLY THE PRESENT INVENTION RELATES TO A PROCES FOR PRODUCING ACRYLIC SYTHETIC FIBES OF A NONCIRCULAR CROSSSECTION IMPROVED IN THE SPARKLE BY WET-SPINNING A SPINNING SOLUTION PREPARED BY DISSOLVING AN ACRYLIC POLYMER IN AN INORGANIC SOLVENT, THROUGH A SPINNERETTE MADE OF A SYNTHETIC RESIN AND HAVING A PARTICULAR SPINNING ORIFICE SHAPE AND THERMAL CONDUCTIVITY, WHILE MAINTAINING A PREDETERMINED JET STRETCHING RATIO.

Jan. 15', 1974 KEITARO 5 1 0 ETAL PROCESS FOR PRODUCING ACRYLIC SYNTHETIC FIBERS OF NONGIRCULAR CROSS-SECTION AND WITH IMPROVED SPARKLE Filed Aug.- 10, 1972 5 Sheets-Sheet 1 Jill. 15, KEITARQ SHIMQDA E'TAL PROCESS FOR PRODUCING ACRYLIC SYNTHETIC FIBERS 0F N'ONCIRCULAR CROSS-SECTION AND WITH IMPROVED SPARKLE 5 Sheets-Sheet 2 ,Filed Aug. 10. 1972 FIG. 3.

Exp. 3

Exp. I

FIG. 4.

m D x E Jan. 15, IT R sHlMODA ETAL PROCESS POR PRODUCING ACRYLIC S'iNTliEl 1C FlBBRS JF NONCERCULAR CROSS-SECTION AND WITH IMPROVED SPARKLE Filed Aug. 10. 1972 5 sheets"sheet 3 ACIFLTV M """1 I M I 1 L 5 EL R I A g u 1' L. J

L; L I 1 recording paper Reading of 3,786,125 PROCESS FOR PRODUCING ACRYLIC SYNTHETIC FIBERS OF NONCIRCULAR CROSS-SECTION AND WITH IMPROVED SPARKLE Keitaro Shimoda, Isamu Obama, and Takamaro Kusunose, Saidaiji, Japan, assignors to Japan Exlan Company Limited, Osaka, Japan Filed Aug. 10, 1972, Ser. No. 279,625 Claims priority, application Japan, Aug. 12, 1971, 46/ 61,202 Int. Cl. B28l1 28/54 US. Cl. 264-177 F 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for producing acrylic synthetic fibers of a noncircular cross-section, improved in sparkle, from a spinning solution prepared by dissolving an acrylic polymer in an inorganic solvent. More particularly the present invention relates to a process for producing acrylic synthetic fibers of a noncircular crosssection improved in the sparkle by wet-spinning a spinning solution prepared by dissolving an acrylic polymer in an inorganic solvent, through a spinnerette made of a synthetic resin and having a particular spinning orifice shape and thermal conductivity, while maintaining a predetermined jet stretching ratio.

Synthetic fibers having a noncircular cross-section are known as to be peculiar with respect to physical properties as brightness, bulkiness and covering power as compared with synthetic fibers having the usual circular crosssection, and therefore various means for their industrial production have already been developed. However, in order to produce acrylic synthetic fibers having a noncircular cross-section from a spinning solution prepared by dissolving an acrylic polymer in an inorganic solvent by the wet-spinning process, it is necessary to increase the jet stretching ratio which is represented as a ratio of the coagulated filament pulling out velocity/ the average flowing velocity of the spinning solution through the sipnning orifice. However, a spinnerette made of a metal is generally high in the thermal conductivity so that the reduction of the temperature of the spinning solution near the spinning orifice is great and it is very difiicult to maintain the above mentioned jet stretching ratio at a predetermined level, Therefore, unless spinning orifices in which the ratio of the long diameter/the short diameter is extremely large are used, it has been difiicult to form any desired noncircular cross-section from spun fibers.

As a method of eliminating such problem, there has been suggested, for example, in French Pat. No. 1,570,- 229, a process for producing fibers of a noncircular crosssection by a wet-spinning process 'by using a spinnerette provided with noncircular spinning orifices and made of a synthetic resin material low in thermal conductivity. According to said French patent, the larger the jet stretching ratio (represented as the ratio of a coagulated filament pulling out velocity/an average flowing velocity of the spinning solution through the spinning orifice), the greater the tendency of the cross-sectional shape of the finally obtained fiber to become noncircular.

We have now found that, in order to impart a more favorable sparkle to the acrylic synthetic fiber to be finally obtained, it is necessary to select not only the jet stretching ratio but also the shape of the spinning orifice.

A principal object of the present invention is to pro vide a novel industrial method of forming acrylic synthetic fiber of a noncircular cross-section, improved in sparkle, by a wet-spinning process.

Another object of the present invention is to deter- United States Patent mine a spinning orifice shape and jet stretching ratio favorable to the production of acrylic synthetic fibers of a noncircular cross-section by using a spinnerette device made of a synthetic resin material.

Other objects of the present invention will become apparent from the following description.

Such objects of the present invention can be attained by extruding a spinning solution prepared by dissolving an acrylic polymer in an inorganic solvent into a coagulating bath through a spinnerette whose thermal conductivity does not exceed 5 10- cal. cmf 'secr -deg." and in which are formed spinning orifices each having a dimensional ratio defined by the following relative Formulae 1 and 2:

1.10b/a1.95 (l) (3/6128 wherein a is the smallest width of the spinning orifice, b is the largest width of the spinning orifice measured in the same direction as of a, and c is the long diameter of the spinning orifice measured in the direction at right angles with the above mentioned a or b, and narrowed in the central part so as to be formed into a fiber filament and taking the filament out of said coagulating bath while maintaining the jet stretching ratio (represented as a ratio of a cogulated filament pulling out velocity/ average flowing velocity of the spinning solution through the spinning orifice) of less than 0.6.

The invention will be explained in more detail by referring partly to the attached drawings wherein:

FIG. 1 exemplifies spinning orifice shapes suitable to work the present invention;

FIG. 2 shows a spinning orifice shape of a spinnerette to melt-spun synthetic fiber filaments to be used as a spinning orifice forming material in making a spinnerette device by a synthetic resin pouring and molding process;

FIG. 3 shows photographs of cross-section of acrylic synthetic fibers obtained by wet-spinning by varying the spinning orifice shape;

FIG. 4 shows photographs of side surfaces of acrylic synthetic fibers obtained by varying the jet stretching ratio;

FIG. 5 is a block diagram of a contrast index measuring apparatus;

FIG. 6 is a plan view of the apparatus showing the formation of the essential part in FIG. 5; and

FIG. 7 is a view for explaining the shape of the peak in the recording paper representing the high light of a tested sample.

Thus, the present invention is directed to the production of acrylic synthetic fibers of a noncircular cross-section having a characteristic sparkle by selecting a material much lower in thermal conductivity than any metal material as spinnerette forming material and specifying the spinning orifice shape and a range of the jet stretching ratio in wet-spinning acrylic synthetic fibers.

According to the invention, there is obtained an acrylic fiber with a cross-sectional shape having a narrow portion in the central part and with improved brightness in acrylic synthetic fibers, by adopting the above mentioned requirements as integrally combined. Therefore, even in case of a partial deviation from the above described peculiar spinning conditions, not only the cross-sectional shape of the finally obtained acrylic synthetic fibers but also the level of the sparkle will fluctuate more than a negligible amount. For example, in case a material higher in thermal conductivity than that recommended in the present invention is selected as a spinnerette forming material and the values of b/ a and c/a representing the shape peculiarity of the spinning orifice are set outside the specified range, the cross-sectional shape of the finally obtained acrylic synthetic fiber will substantially approach to a circular shape and the level of the sparkle will be considerably reduced. Further, if the jet stretching ratio is set in a range exceeding 0.6, not only the macroscopic form peculiarity but also the surface form of the microscopic order of the finally obtained fiber of noncircular cross-section will vary and the luster itself will qualitatively vary.

The present invention has its fundamental basis in the fact that a peculiar spinning orifice shape, narrow at the center, is effective to improve the sparkle in the spun fiber even under the state in which the jet stretching ratio is substantially reduced. This was discovered by noting the fact that, when the jet stretching ratio is reduced with a view to smoothing the surface form of the finally obtained acrylic synthetic fiber of a concircular cross-section, the cross-sectional shape of the spun fiber will approach a circular shape substantially in proportion to the reduction of the jet stretching ratio.

Any material having a thermal conductivity not more than X10 cal.- cmf -secr -degr can be selected without any special limitation for the material forming the spinnerette to be used in the present invention. However, in consideration of the strength required in the practical use or the ease of manufacture, it is preferable to use a thermosetting synthetic resin material in which the thermodeformation temperature defined in ASTM (The American Society for Testing Materials) D648 is above 70 C. and the bending strength defined in ASTM D790 is not less than 700 kg./cm. such as a polyether resin, polycarbonate resin, phenol resin or epoxy resin.

Spinning orifice shapes preferable in working the present invention are exemplified in FIG. 1 in which a represents the smallest width of the spinning orifice, b represents the largest width of the spinning orifice measured in the same direction as a, and 0 represents the long diameter of the spinning orifice measured in the direction at right angles with the above mentioned a or b. As a means of forming a peculiar spinning orifice having such narrow central part, it is possible to adopt a method in which a boring tool of the same cross-sectional shape as of the spinning orifice is used as seen in the ordinary spinnerette device made of a metal. However, as another method, it can be formed by synthetic resin casting by the embedding technique mentioned in Japanese patent 'publication No. 2,328/1970 by using, as a spinning orifice forming material, a synthetic fiber filament obtained by melt-spinning a fiber forming polymer through a spinning orifice having a cross-sectional shape satisfying the conditions of the below mentioned relative Formulas 3 and 4:

1.2b'/a'2.5 (3) c'/ 1210.0

wherein a is the smallest width of the spinning orifice, b is the largest Width of the spinning orifice measured in the same direction as a, and c' is the long diameter of the spinning orifice measured in the direction at right angles with the above mentioned a or b.

The term acrylic polymer as used in the present in- 'vention is a fiber-forming polymer having acrylonitrile as a main component and means inclusively a polyacrylonitrile, a copolymer of more than 70% by weight acrylonitrile with another vinylic monomer copolymerizable with acrylonitrile or a polymer blend of such polymer with another polymer.

As inorganic solvents which can be used in the present invention for dissolving such acrylic polymer to prepare a spinning solution, there can be enumerated concentrated aqueous solutions of such thiocyanates as sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate and calcium thiocyanate, mixtures of these thiocyanates, concentrated aqueous solutions of such inorganic salts as zinc chloride and lithium chloride and concentrated aqueous solutions of such inorganic acids as sulfuric acid and nitric acid. On the other hand, for the 00- agulating bath, there can be used water or an aqueous solution of the above mentioned inorganic salt or inorganic acid of a concentration less than 35%.

The acrylic synthetic fiber having a noncircular crosssection and wet-spun by the method of the present invention can be subjected to the usual after-treatment such as washing, stretching, compacting, drying and heat-relaxing in the ordinary manner after the fiber formation in the coagulating bath.

In the present invention, a contrast index and 60-degree mirror surface luster (G5 are adopted as scales for quantitatively evaluating the sparkle of the finally obtained acrylic synthetic fiber of a noncircular crosssection. These terms are defined as follows:

(1) 60-degree mirror surface luster (G A fiber tow to be measured has the crimps stretched under tension while being heated, is pulled and arranged in parallel and is fixed at both ends on a cardboard to prepare a rectangular test piece of 6 cm. X 4.5 cm. By using a luster meter Model GM-S (manufactured by Murakami Coloring Technical Laboratory) and according to 11$ Z-874l, the fibers are measured by irradiating them with rays so that a plane including incident rays and reflected rays may be made to coincide with the axes of the fibers and the angle of incidence of the irradiating rays may be 60 degrees with the direction of pulling and arranging the fibers.

(2) Contrast index: The contrast index can be determined by measuring a sample S by using a scanning type microscopic luster meter consisting of a current source stabilizer ST, voltage stabilizer EST, light source L, magnifying lens optical system El, movable photoelectric multiplying tube R, amplifier A and register system REC shown in the block diagram in FIG. 5. To explain more particularly by also using FIG. 6, the fiber tow to be measured is pulled and arranged in parallel and is pasted to a cardboard to prepare a sample plate 27. The sample plate 27 is positioned on a disk-shaped sample stand 28 so that the pulling and arranging direction of the fiber two may be vertical to the horizontal plane of the diskshaped sample stand 28. A light source 29 is of such optical system that irradiating rays may proceed in parallel with the horizontal plane of the disk-shaped sample stand 28 and their angle of incidence may be 45 degrees with the fiber two to be tested. The optical axis of a photoelectric multiplying tube 21 movable in parallel with the horizontal plane of the disk-shaped sample stand 28 is provided to coincide with a. normal erected on the sample surface at the point of incidence, and a magnifying lens optical system EL consisting of an objective 26 of a magnification of 11.1 times, lens barrel 25 and camera 24 is provided between the sample fiber two and photoelectric multiplying tube 21 so that the image of the sample may be focused on a frosted glass plate 23 fixed to the camera 24. A rectangular slit 22 which is 1.0 mm. long in the fiber two pulling and arranging direction and 0.2 mm. long in the direction at right angles with the fiber two pulling and arranging direction is formed and said photoelectric multiplying tube 21 is moved by 20 mm. While maintaining a constant velocity of 8 mm. per minute along the sample image on the frosted glass plate 23. The electric output of the photoelectric multiplying tube 21 is fed to such register REC having a full scale width of 0 to 5- mv. as, for example, a register Model LER-12A manufactured by Yokokawa Electric Machinery Manufactory, Ltd. through an amplifier A in which the fed voltage is made constant in advance by a high voltage controller EST and low voltage controller ST and is recorded on a recording paper sheet moving by maintaining a constant velocity of 60 mm. per minute in said part.

Thus, as examplified in FIG. 7, fine high lights reflected from the sample fiber two are recorded as peaks H H H H, on the recording paper and dark parts between the high lights are recorded as valleys L L L L between the peaks. When the average heights per unit length of the recording paper of the peaks and the valleys between the peaks are respectively h and 1,, in FIG. 7, the contrast index in the present invention will be defined as follows:

Contrast index log n The larger the contrast index of the fiber two, the clearer and stronger the microscopic spot light pencil reflected ttrom the sample surface and the more remarkable the visible sparkle.

Examples of the present invention but the scope of the present invention is not limited to such specific examples, in which the parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 An acrylic polymer of a molecular weight of 58,000 made by copolymerizing 91% acrylonitrile and 9% methyl acrylate was dissolved in an aqueous solution of sodium thiocyanate of a concentration of 46% to prepare. a spinning solution of a polymer concentration of 11%. The spinning solution was heated to 70 C. and was extruded into a coagulated bath consisting of an aqueous solution of sodium thiocyanate of a concentration of at a temperature of 3 C. by using a spinnerette (of a thermal conductivity of 4X10 cal. -sec.- 'cm.- 'deg. having spinning orifices shown in A in FIG. 1 and made of an epoxy resin by the method mentioned in Japanese patent publication No. 2,328/ 1945 so as to be formed into a fiber filament and the filament was pulled out of the coagulating bath while maintaining the jet stretching ratio at 0.5. Then the obtained fiber filament was washed with water, stretched two times the length in cold water and then 5 times the length in boiling water. The excess water contained in the fiber was press-squeezed out with nip rollers, and the water content Was adjusted to be 60 on the dry weight of the fiber. Then the fiber was dried to be compacted under no tension in a moisture-adjusted atmosphere at a dry-bulb temperature of 120 C. and a wet-bulb temperature of 80 C. and was heat-relaxed in saturated steam at 117 C. to make an acrylic synthetic fiber of a noncircular cross-section of a monofilament fineness of deniers. The characteristics of the obtained acrylic synthetic fibers of the noncircular cross-section are indicated in Table 1 and the cross-sectional shapes of typical fibers are shown in FIG. 3.

TABLE I Spinning orifice GO-degree It will be understood from Table 1 and FIG. 3 that, in the tested fiber of each of the experiments Nos. 1, 2, 4 and 5 in which the spinning orifice dimensional ratios b/rz and c/a satisfy the ranges recommended in the present invention, the cross-sectional shape has a preferred noncircular shape narrowed in the central part. The 60- degree mirror surface luster and contrast index values show the sparkle of the fiber with a preferable contrast. However, in the tested fiber of each of the experiments Nos. 3 and 6 in which the spinning orifice dfiiensional ratios deviate from the range specified in the present invention, the cross-sectional shape maintains the jet stretching ratio at 0.5 but is close to a circular shape and the sparkle represented by the 60-degree mirror surface luster or contrast index is evidently reduced.

EXAMPLE 2 An acrylic polymer of a molecular weight of 58,000 made by copolymerizing 89% acrylonitrile and 11% methyl acrylate was dissolved in an aqueous solution of sodium thiocyanate of a concentration of 46% to prepare a spinning solution of a polymer concentration of 12%. The spinning solution was heated to 70 C., and extruded into an aqueous solution of sodium thiocyanate of a concentration of 10% at a temperature of 3 C. through a spinnerette (of a thermal conductivity of 4X10- cal.- cm.- sec.- deghaving spinning orifice dimensional ratios of b/a of 1.75 and c/a of 9.75, made of an epoxy resin and shown in A in FIG. 1, so as to form coagulated filaments, which were pulled out of the coagulating bath while varying the jet stretching ratio as indicated in Table 2. Then the obtained coagulated filaments are washed with water, stretched, dried to be compacted and heat-relaxed according to the same conditions as in Example 1 to make an acrylic synthetic fiber of a noncircular cross-section of a monofilament fineness of 15 deniers. The characteristics of the fibers are indicated in Table 2 and the side surface states of the typical fibers are shown in FIG. 4.

In the tested fiber of each of the experiments Nos. 7 and 8 in which the jet stretching ratio is higher than the preferable range recommended in the present invention, many fine pleat-shaped bends are formed on the surface and the 60-degree mirror surface luster or contrast index is also reduced.

On the other hand, for comparison, the same spinning solution was spun, stretched, dried to be compacted and heat-relaxed under the same spinning conditions as in the above mentioned Example 2, except that the material of the spinnerette was changed to a metal having platinum as a main component from the epoxy resin in the above mentioned Example 2, to make an acrylic synthetic fiber of a monofilament fineness of 15 deniers. In each of the acrylic synthetic fibers obtained in this control, the crosssection was close to a circular shape and the sparkle was insufficient. As typical examples, the 60-degree mirror surface luster of the acrylic synthetic fiber spun by setting the jet stretching ratio at each of 1.00 and 0.23 is shown in Table 3.

TABLE 3 60-degree Experi- Jet mirror ment stretching surface N 0. ratio luster What we claim is:

1. A process for producing acrylic synthetic fibers of a noncircular cross-section improved in sparkle characterized by extruding a spinning solution prepared by dissolving an acrylic polymer in an inorganic solvent into a coagulating bath through a spinnerette whose thermal conductivity does not exceed 5X10" cal. cmr sec.- deg.-

and which has spinning orifices each having a dimensional ratio defined by the relative Formulas 1 and 2:

c/ag8 1 wherein a is the smallest width of the spinning orifice, b is the largest width of the spinning orifice measured in the same direction as of a, and c is the long diameter of the spinning orifice measured in the direction at right angles with the above mentioned a or b and narrowed in the central part so as to be formed into a fiber filament and taking the filament out of said coagulating bath while maintaining the jet stretching ratio, which is defined as the ratio of coagulated filament pulling out velocity/ average flowing velocity of the spinning solution through the spinning orifice, between 0.23 and 0.6.

2. A process as claimed in claim 1 wherein the acrylic polymer is an acrylic copolymer consisting of not less than 70% by weight of acrylonitrile and the remainder being one or more vinyl monomers copolymerizable with acrylonitrile.

3. A process as claimed in claim 1 wherein the spinnerette has a thermodeformation temperature above 70 C. and a bending strength not less than 700 kg./cm.

References Cited UNITED STATES PATENTS 1,902,953 3/ 1933 Hazell 264--l77 F 2,373,892 4/1945 Hickey 264207 2,816,349 12/1957 Pamm et al. 264177 F 2,831,748 4/1958 Finlayson et al. 264177 F 2,838,365 6/1958 Jarrett 264-207 3,131,428 5/1964 Mika 264-177 F 3,621,087 11/1971 Shimamura et al. 264-182 3,673,053 6/ 1972 Shimoda et al. 264-482 3,676,540 7/ 1972 Story et al. 264-182 JAY H. WOO, Primary Examiner US. Cl. X.R. 

